1. Field of the Invention
The disclosure generally relates to an imaging system, and more particularly to a lens shading correction (LSC) system for an imaging system.
2. Description of Related Art
In an imaging system, lens shading (or vignetting) is a phenomenon that causes pixels located away from a center pixel of a pixel array to have a lower pixel signal value even when all pixels are exposed to the same illumination condition. As a result, brightness of an image can fall off from a center region to corners. In other words, a maximum brightness may be at or around the center and decrease along a radial direction of the pixel array. The lens shading phenomenon may be presented, for example, in the contexts of lens mechanisms, optics, sensor pixels, ray traveling distance, aperture effect and/or ray incident angle to pixels.
Lens shading correction (LSC) is commonly proposed to compensate for the brightness falloff by way of applying different gains, particularly for the pixels away from the center of the pixel array. One drawback of conventional LSC schemes is induced color shading (or color non-uniformity) due to use of a single light source to perform correction. Even when multiple light sources are used, the falloff may correspond not to a monotonic change but rather to an abrupt drop from high color-temperature to low color-temperature light sources. Moreover, metamerism issues may occur, causing confusion in performance of lens shading correction via color temperature because two (or more) light sources may have similar color temperatures but have very different spectra.
For reasons including the fact that conventional LSC schemes have been unable effectively to solve the lens shading phenomenon, a need has arisen to propose a novel LSC system to overcome drawbacks encountered in such conventional LSC schemes.